The image compression methods that are prevalent today include JPEG (Joint Photographic Experts Group) and JPEG 2000 standardized by the ISO (International Standards Organization).
In recent years, studies have been underway on encoding methods that allow images to be split into a plurality of bands by a so-called filter bank combining a high-pass filter and a low-pass filter so that each band of the image may be coded individually. Of these encoding methods, wavelet transform coding is free from block distortion that can affect DCT (Discrete Cosine Transform) under high-compression conditions; the method is thus attracting attention as a new technique to replace DCT.
JPEG 2000, of which the international standardization was completed in January 2001, is a method that combines the above-mentioned wavelet transform with highly efficient entropy encoding (i.e., bit modeling and arithmetic encoding in units of a bit plane). As such, JPEG 2000 is a significant improvement over JPEG in terms of encoding efficiency.
JPEG 2000, selected also as the standard codec for the digital cinema standard (DCI (Digital Cinema Initiative) Standard), has started to be used in compressing the moving images of movies and the like. A number of manufacturers have started to introduce products that apply JPEG 2000 to such devices as surveillance cameras, on-site coverage cameras, and security recorders.
However, since JPEG 2000 involves encoding and encoding basically in units of a picture, attempts to achieve low delays in real-time transmission and reception entail a delay of at least one picture in encoding and decoding each.
The same applies not only to JPEG 2000 but also to such codecs as AVC (Advanced Video Coding) Intra and JPEG. Recently, means have been proposed for shortening delay time by dividing the screen into several rectangular slices or tiles and encoding and decoding each of them independently (e.g., see Patent Document 1).